M. J. Blish - 553 
TABLE I. 
Total N not 
Method of treatment using 50 cc. portions of extract. precipitated. 
: gm. 
1. 1 ec. Merck’s 5 per cent colloidal iron ppt. at room tem- 
perature, followed by 1 cc. of concentrated MgSO, 
BU td SNE PO cit 102 a! Rye micas ad Ree Aes As, sable 0.00266 
2. Same as No. 1 with precipitation at boiling temperature. . 0.0033 
3. Precipitation with 10 cc. of 10 per cent phosphotungstic 
acid after making strongly acid with HCl.............. 0.0010 
eye recwpiation with tannic acid. . 2. 9s...5 ee sa Beee ee 0.0012 
Memneeer Pe Gee HOG 3/2157 Sages a eiiecde Seat rae, pwr a Peed 0.0008 
The details of the copper method as used on flour extracts in 
this laboratory are presented in the following experiments. 
Expervment I. 
- Ceretana, a standard patent flour milled by the Bozeman 
Milling Company of Bozeman, Montana, was used in the pre- 
liminary work, which consisted of determining the proper pro- 
portions of flour to water for the extraction, the length of time 
of extraction, and a comparison of the copper method with the 
other methods mentioned earlier in this paper with respect to the 
“total non-protein nitrogen’ determined by other methods. 
Distilled CO,-free water, saturated with toluene, was used for all 
extractions. After trying various proportions of flour to water, 
20 parts of water to 1 of flour was decided upon as a convenient 
proportion to use for extractions. Extractions were carried on 
for varying lengths of time, using portions of 20 gm. of flour to 
400 cc. of water in 500 cc. Erlenmeyer flasks. The flasks were 
shaken vigorously every 15 minutes, for periods of 2, 3, 4, 5, 6, 
and 12 hours, respectively. At the end of each period the. ex- 
tract was filtered through paper, the proteins were precipitated 
by treating 50 ce. of extract with 15 cc. of 0.1 N NaOH, followed 
by 16 cc. of 0.1 N CuSO,, and total nitrogen was determined in 
the filtrate from the copper precipitation. The amount was 
found to be the same for the 2 hour extraction as for the 12 hour 
period, and therefore a minimum extraction period of 2 hours 
was adopted. Perhaps the most satisfactory method for the 
